In recent years, development of a ferroelectric memory (FeRAM) that holds information in a ferroelectric capacitor structure by using polarization inversion of ferroelectrics has been pursued. A ferroelectric memory especially attracts attention because it is a nonvolatile memory which does not lose information held therein even when the power supply is cut off, and realization of high integration density, high-speed drive, high durability and low power consumption can be expected from it.
As the material of the ferroelectric film constituting the ferroelectric capacitor structure, a ferroelectric oxide having a perovskite crystal structure such as a PZT (Pb(Zr, Ti)O3) film with a large remnant polarization amount, for example, of about 10(μC/cm2) to 30(μC/cm2), and an SBT (SrBi2Ta2O9) film is mainly used.
In a capacitor structure, especially, in a ferroelectric capacitor structure, it is known that the characteristics of a ferroelectric film degrades by moisture entering from an outside through an interlayer insulation film having high affinity with water such as a silicon oxide film. Namely, the moisture entering from the outside is decomposed into hydrogen and oxygen in the high-temperature process at the time of deposition of an interlayer insulation film and metal wiring. If the hydrogen enters the ferroelectric film, it reacts with oxygen in the ferroelectric film to form oxygen deficiency in the ferroelectric film to degrade crystallinity. A similar phenomenon occurs due to long-term use of a ferroelectric memory. As a result, performance degradation of the ferroelectric capacitor structure such as reduction in the remnant polarization amount and dielectric constant of the ferroelectric film, or the like occurs. Further, such entry of hydrogen sometimes degrades the performances of not only the ferroelectric capacitor structure but also the transistor and the like.
Accordingly, in order to prevent entry of moisture/hydrogen into the ferroelectric capacitor structure, the ferroelectric capacitor structure is covered with a thin film (hydrogen diffusion prevention film) of alumina (Al2O3) or the like, having the function of preventing diffusion of hydrogen, and in order to form an insulation film with an extremely low moisture content as an interlayer insulation film covering the ferroelectric capacitor structure via the hydrogen diffusion prevention film, a silicon oxide film is formed by a plasma CVD method using a source gas including, for example, TEOS. By forming the silicon oxide film as the interlayer insulation film under a so-called extremely low moisture content condition, entry of moisture/hydrogen into the ferroelectric capacitor structure can be prevented as much as possible in corporation with the hydrogen diffusion prevention film.
However, the silicon oxide film formed under the above described extremely low moisture content condition has the in-plane film thickness distribution of about 5%, and even when the silicon oxide film is formed to cover the ferroelectric capacitor structure as the interlayer insulation film, and thereafter, surface flattening is performed for it by polishing it with a Chemical Mechanical Polishing method (Chemical-Mechanical Polishing: CMP method), its in-plane film thickness distribution is large. Therefore, the influence of the ferroelectric capacitor structure on the ferroelectric characteristics, variation in the contact resistance, and the like become problems.